1. Field of the Invention
The present invention relates to a pneumatic tire, and in particular, it relates to a pneumatic tire in which a sipe is formed in a land part of a tread surface.
2. Description of the Related Art
In a land part of a tread surface of a pneumatic tire, for the purpose of enhancing a noise performance, a wet performance or the like, there may be the case where a sipe extending in a tire width direction is provided. Conventionally, in those provided with such a sipe in the width direction, it is known that by forming a waveform sipe in a bottom part of a straight sipe, the sipe shape is changed from a straight line to a waveform form over the middle of wear to the end of wear, thereby raising an edge effect in the end of wear (see, for example, JP-A-2004-161166, JP-A-2006-56502 and JP-A-2007-314168).
In the foregoing conventional sipes, the waveform sipe provided in the bottom part of the straight sipe was formed over the whole of the sipe length direction. When the whole of the bottom part is formed in a waveform shape in such a way, on the occasion in which after vulcanization molding of a tire, a sipe molding blade of a die is removed from a tread part, die releasability is poor, so that a problem such as chipping of rubber is easily caused in the sipe surroundings. Such defectiveness of die releasability is not substantially problematic with respect to tires with low rubber hardness such as studless tires, whereas it is a serious problem with respect to tires with high rubber hardness such as all-season tires and summer tires.
Now, in pneumatic tires, there is taken ground contact pressure distribution in which at the time of normal running, especially at the time of braking, the ground contact pressure is locally raised in a shoulder region of a tread, in particular, on the ground contact end side within a shoulder region. When the ground contact pressure is locally raised in this way, it may be considered that in the subject portion, collapse of a sipe becomes large, and the movement (deformation) of a block becomes large, whereby a braking performance and a wear performance are adversely affected. However, according to the foregoing conventional sipe configurations, since the sipe has a fixed shape in the length direction, the collapse of a sipe to be caused due to a local rise of the ground contact pressure on the ground contact end side within such a shoulder region could not be suppressed.